1. Field of the Invention
The present invention relates to an arrangement for the frequency-selective suppression of high frequency signals. In particular, it relates to an arrangement for suppressing undesired signal frequencies within a transmitting and/or receiving device.
2. Prior Art
In transmitting and/or receiving devices, to generate or process high frequency signals, auxiliary signals are often needed that are generated with the aid of an oscillator. One example of this is the frequency signal of a receiving oscillator (local oscillator) in a receiving device on the superheterodyne principle. Such auxiliary signals, however, should as a rule not be capable of escaping, or should be capable of escaping only within a narrowly defined frequency range, from the circuit component for which they are needed. To prevent these auxiliary signals from leaving the prospective circuit component, it is known to use shielding baffles, shielding housings, and also filter means as options. The better the suppression of undesired signal frequencies is supposed to be, the greater is the requisite effort and expense, as a rule.
Over the course of technological development in the context of high-frequency technology, increasingly more circuits in microline technology are employed. It is possible in principle also to make filter circuits for suppressing undesired signal frequencies by this technology. However, they often lack the requisite quality, selectivity or selection for complete suppression of undesired signal frequencies. High-frequency filters that have higher quality are known in the form of cavity resonators. It is also known to combine microline technology circuits with such cavity resonators. This makes it possible, even in a component group made by microline technology, to achieve a filter circuit of the highest possible quality. One example of such an arrangement is described in International Patent Disclosure WO 92/13371. This reference relates to an arrangement and a method for coupling a microline circuit to a cavity resonator. The arrangement includes a substrate plate, with the microline circuit provided on one side and the ground plane provided on the other. A cavity resonator is also present. According to this reference, the microline circuit is coupled to the cavity resonator with the aid of a slit, provided in the ground plane, and a planar radiator, which is disposed between the ground plane and the cavity resonator.
Another transition from a microline circuit to, in this case, a hollow conductor is known from German Patent Disclosure DE 42 41 635 Al. Here the microline changes over to a unilateral suspended-substrate line, and a space located above this line on the opposite side of the substrate is widened to a cross section equivalent to the cross section of the adjoining hollow conductor.
In these known couplings, difficulties can arise above all from mechanical strains between the substrate of the microline circuit and the hollow conductor or cavity resonator. These strains are due to different temperature-dependent coefficients of expansion of the different materials. The known couplings are often also difficult to achieve because the assembly and connection of the microline with the cavity resonator must typically be done highly exactly. Another disadvantage that can be named is that in the filter arrangement of WO 92/13371, the high frequency signals to be filtered are coupled in and out via one and the same coupling terminal. It cannot be entirely precluded that at least some undesired high frequency signals will be transmitted directly from the input of the filter arrangement to the output.